EP0920461A1

EP0920461A1 - Components and catalysts for the polymerization of olefins

Info

Publication number: EP0920461A1
Application number: EP98930782A
Authority: EP
Inventors: Giampiero Morini; Giulio Balbontin; John Chadwick; Antonio Cristofori; Enrico Albizzati
Original assignee: Montell Technology Co BV
Current assignee: Basell Technology Co BV
Priority date: 1997-06-09
Filing date: 1998-06-02
Publication date: 1999-06-09
Anticipated expiration: 2018-06-02
Also published as: CN1236374A; ITMI971349A1; ATE207086T1; ES2164436T3; NO990575L; BR9804961A; US6281301B1; WO1998056834A1; ITMI971349A0; TR199900264T1; DE69802059D1; EP0920461B1; IT1292108B1; NO990575D0; JP2000516989A; CA2261667A1; AU8109698A; JP4306808B2; KR20000068056A; DE69802059T2

Abstract

The present invention relates to a solid catalyst component for the polymerization of olefins CH2=CHR is which R is hydrogen or a hydrocarbyl radical with 1-12 carbon atoms, comprising a titanium compound, having at least a Ti-halogen bond and an electron donor compound supported on an Mg halide, in which said electron donor compound is selected from esters of malonic acids of formula (I), wherein R1 is a C1-C20 linear or branched alkyl, C3-C20 alkenyl, C3-C20 cycloalkyl, C6-C20 aryl, arylalkyl or alkylaryl group; R2 is a C1-C20 linear alkyl, C3-C20 linear alkenyl, C6-C20 aryl, arylalkyl or alkylaryl group; R3 and R4 are independently selected from the group consisting of C1-C3 alkyl, cyclopropyl, with the proviso that when R1 is C1-C4 linear or branched alkyl or alkenyl, R2 is different from R1. Said catalyst components when used in the polymerization of olefins, and in particular of propylene, are capable to give high yields and polymers having high insolubility in xylene.

Description

"COMPONENTS AND CATALYSTS FOR THE POLYMERIZATION OF OLEFINS"

The present invention relates to catalyst components for the polymerization of olefins,

to the catalyst obtained therefrom and to the use of said catalysts in the polymerization of

olefins CH₂=CHR in which R is hydrogen or a hydrocarbyl radical with 1-12 carbon atoms. In

particular the present invention relates to catalyst components, suitable for the stereospecific

polymerization of olefins, comprising a titanium compound having at least a Ti-halogen bond

and an electron donor compound selected from esters of malonic acid having a particular

formula supported on a Mg halide. Said catalyst components used in the polymerization of

olefins, and in particular of propylene, are capable to give polymers in high yields and with high isotactic index expressed in terms of high xylene insolubility.

The use of some esters of malonic acid as internal electron donors in catalysts for the polymerization of propylene is already known in the art.

In EP-A-45977 is disclosed the use of an ester of the malonic acid (diethyl

diisobutylmalonate) as internal donor of a catalyst for the polymerization of olefins. EP-A-

86473 discloses a catalyst for the polymerization of olefins comprising (a) an alkyl compound,

(b) an electron donor compound having certain reactivity features towards MgCl and (c) a

solid catalyst component comprising, supported on MgCl , a Ti halide and an electron donor

selected from many classes of ester compounds including malonates. In particular, the use of

diethyl allylmalonate and di-n-butyl malonate as internal donors in a catalyst for the

polymerization of propylene is exemplified. From EP-A-86644 is known the use of diethyl n-

butyl malonate and diethyl isopropylmalonate as internal donors in Mg-supported catalysts for

the polymerization of propylene in which the external donor is a heterocyclic compound or a

ketone. The European patent EP-B-125911 discloses a process for producing (co)polymers which comprises (co)polymerizing at least one olefin, optionally with a diolefin, in the presence

of a catalyst composed of (a) a solid catalyst component containing Mg, Ti and an electron

donor compound selected from esters of polycarboxylic acids, (b) an organometallic compound

of a metal selected from group I to HI of the periodic table, and (c) an organosilicon compound

having a Si-O-C or a Si-N-C bond. Examples of preferred esters compounds include diethyl

methylmalonate, diethyl butylmalonate, diethyl phenylmalonate, diethyl diethylmalonate, and

diethyl dibutylmalonate. Only the use of a catalyst containing diethyl phenylmalonate has been exemplified in the preparation of polypropylene.

However, a common drawback experienced in the use of the above mentioned

malonates was represented by a poor polymerization yield and/or a not suitable isotactic index of the final polymer.

JP-08157521 relates to a process for preparing a solid catalyst component for polymerization of olefins which is characterized by contacting a solid catalyst component

produced by the reaction among a magnesium compound, a titanium compound and an halogen

compound, with one or more of electron donating compounds represented by the general

formula:

wherein R_c and R_ are, independently selected from the group consisting of: a straight-chain or

branched hydrocarbon group having 1-10 carbon atoms, and R_a and R_b are independently selected from an aliphatic or cyclic saturated hydrocarbon group containing one or more

secondary or tertiary carbons and having 3-20 carbon atoms. According to this patent the fact

that the substituents R_a and Rb are branched is very important.

It has now surprisingly been found that another class of malonate esters wherein one

substituent in 2 position is selected from a linear alkyl, alkenyl, aryl, arylalkyl or alkylaryl

group, when used as an internal electron donor, leads to higher polymerization yields compared

to those obtainable by using the electron donors of the prior art still maintaining very high

stereoselectivity. This is particularly surprising in view of the direct teaching of JP-A- 08157521, which excluded this class of compounds.

It is therefore an object of the present invention a solid catalyst component for the

polymerization of olefins CH₂=CHR in which R is hydrogen or a hydrocarbyl radical with 1-12 carbon atoms, comprising a titanium compound, having at least a Ti-halogen bond, and an electron donor compound supported on a Mg halide, in which said electron donor is selected

from esters of malonic acids of formula (I):

wherein Ri is a Cι-C₂₀ linear or branched alkyl, C -C₂o alkenyl, C₃-C₂₀ cycloalkyl, C₆-C₂o aryl,

arylalkyl or alkylaryl group; R is a Cj-C o linear alkyl, C -C₂₀ linear alkenyl, C₆-C₂₀ aryl,

arylalkyl or alkylaryl group; R and R₄ are independently selected from the group consisting of

Cι-C₃ alkyl, cyclopropyl, with the proviso that when Rj is Cι-C linear or branched alkyl or alkenyl, R₂ is different from Rj; preferably R is primary linear Cι-C ₀ alkyl or a primary C₆-C₂o

arylalkyl group.

These new electron donors permit to obtain higher yields in the polymerization process

with respect to the catalyst containing the malonates known in the art.

Specific examples of preferred disubstituted malonates compounds are:

diethyl-2,2-dibenzylmalonate, dimethyl-2-n-butyl-2-isobutylmalonate,

diethyl-2-n-butyl-2-isobutylmalonate, diethyl-2-isopropyl-2-n-butylmalonate, diethyl-2-methyl-2-isopropylmalonate, diethyl-2-methyl-2-isobutylmalonate,

diethyl-2-isobutyl-2-benzylmalonate.

The magnesium halide is preferably MgCl₂ in active form which is widely known from the patent literature as a support for Ziegler-Natta catalysts. Patents USP 4,298,718 and USP

4,495,338 were the first to describe the use of these compounds in Ziegler-Natta catalysis. It is known from these patents that the magnesium dihalides in active form used as support or co-

support in components of catalysts for the polymerization of olefins are characterized by X-ray

spectra in which the most intense diffraction line that appears in the spectrum of the non-active

halide is diminished in intensity and is replaced by a halo whose maximum intensity is

displaced towards lower angles relative to that of the more intense line.

The preferred titanium compounds used in the catalyst component of the present

invention are TiCl₄ and TiCl₃; furthermore, also Ti-haloalcoholates of formula Ti(OR)_n._yX_y,

where n is the valence of titanium and y is a number between 1 and n, can be used.

The preparation of the solid catalyst component can be carried out according to several

methods. According to one of these methods, the magnesium dichloride in an anhydrous state, the

titanium compound and the electron donor compound of formula (I) are milled together under

conditions in which activation of the magnesium dichloride occurs. The so obtained product

can be treated one or more times with an excess of TiCl at a temperature between 80 and

135°C. This treatment is followed by washings with hydrocarbon solvents until chloride ions

disappeared.

According to a further method, the product obtained by co-milling the magnesium

dichloride in an anhydrous state, the titanium compound and the electron donor compound of

formula (I) is treated with halogenated hydrocarbons such as 1 ,2-dichloroethane, chlorobenzene, dichloromethane etc. The treatment is carried out for a time between 1 and 4

hours and at temperature of from 40°C to the boiling point of the halogenated hydrocarbon.

The product obtained is then generally washed with inert hydrocarbon solvents such as hexane.

According to another method, magnesium dichloride is preactivated according to well

known methods and then treated with an excess of TiCl at a temperature of about 80 to 135°C

which contains, in solution, an electron donor compound of formula (I). The treatment with

TiCl₄ is repeated and the solid is washed with hexane in order to eliminate any non-reacted

TiC .

A further method comprises the reaction between magnesium alcoholates or

chloroalcoholates (in particular chloroalcoholates prepared according to U.S. 4,220,554) and an

excess of TiCl₄ containing the electron donor compound (I) in solution at a temperature of

about 80 to 120°C.

According to a preferred method, the solid catalyst component can be prepared by

reacting a titanium compound of formula Ti(OR)_n-_yX_y, where n is the valence of titanium and y is a number between 1 and n, preferably TiCl , with a magnesium dichloride obtained by

dealcoholation of an adduct of formula MgCl₂»pROH, where p is a number between 0, 1 and 6

and R is a hydrocarbon radical having 1-18 carbon atoms. The adduct can be suitably prepared

in spherical form by mixing alcohol and magnesium chloride in the presence of an inert

hydrocarbon immiscible with the adduct, operating under stirring conditions at the melting

temperature of the adduct (100-130°C). Then, the emulsion is quickly quenched thereby

causing the solidification of the adduct in form of spherical particles. Examples of spherical

adducts prepared according to this procedure are described in USP 4,399,054. The so obtained

adduct can be directly reacted with the Ti compound or it can be previously subjected to

thermal controlled dealcoholation (80-130°C) so as to obtain an adduct in which the number of

moles of alcohol is generally lower than 2.5 preferably between 0,1 and 1,5. The reaction with

the Ti compound can be carried out by suspending the adduct (dealcoholated or as such) in cold

TiCl₄ (generally 0°C); the mixture is heated up to 80-130°C and kept at this temperature for

0,5-2 hours. The treatment with TiCl can be carried out one or more times. The electron donor

compound of formula (I) can be added during the treatment with TiCl . The treatment with the electron donor compound can be repeated one or more times.

The preparation of catalyst components in spherical form are described for example in

EP-A-395083, EP-A-553805, EP-A-553806.

The solid catalyst components obtained according to the above method show a surface

area (by B.E.T. method) generally between 20 and 500 m²/g and preferably between 50 and 400

m²/g, and a total porosity (by B.E.T. method) higher than 0,2 cm³/g preferably between 0,2 and

0,6 cm³/g. A further method to prepare the solid catalyst component of the invention comprises

halogenating magnesium dihydrocarbyloxide compounds, such as magnesium dialkoxide or

diaryloxide, with solution of TiCl₄ in aromatic hydrocarbon (such as toluene, xylene etc.) at

temperatures between 80 and 130°C. The treatment with the TiCl in aromatic hydrocarbon

solution can be repeated one or more times, and the electron donor compound of formula (I) is

added during one or more of these treatments.

In any of these preparation methods the desired electron donor compound of formula (I)

can be added as such or, in an alternative way, it can be obtained in situ by using an appropriate

precursor capable to be transformed in the desired electron donor compound by means, for

example, of known chemical reactions such as esterification, transesterification etc. Generally, the electron donor compound of formula (I) is used in molar ratio with respect to the MgCl₂ of from 00.1 to 1 preferably from 0,05 to 0,5.

The solid catalyst component according to the present invention are converted to the

catalysts for the polymerization of olefins by reacting them with organoaluminium compounds according to known methods.

In particular, it is an object of the present invention a catalyst for the polymerization of

olefins CH₂=CHR, in which R is hydrogen or a hydrocarbyl radical with 1-12 carbon atoms,

comprising the product of the reaction between:

(i) a solid catalyst component comprising a titanium compound having at least a Ti-halogen

bond, and an electron donor compound supported on a Mg halide in active form, in

which said electron donor compound is selected from esters of malonic acids of formula

(I):

wherein Ri is a C1-C20 linear or branched alkyl, C3-C20 alkenyl, C₃-C₂o cycloalkyl, C₆-C₂₀

aryl, arylalkyl or alkylaryl group; R₂ is a Cι-C₂₀ linear alkyl, C₃-C o linear alkenyl, C -C₂o aryl, arylalkyl or alkylaryl group; R₃ and R are independently selected from the group

consisting of C]-C₃ alkyl, cyclopropyl, with the proviso that when Rj is Cι-C linear or

branched alkyl or alkenyl, R₂ is different from Rj; preferably R₂ is primary linear C₁-C₂₀ alkyl or a primary C₆-C₂o arylalkyl group, (ii) an alkylaluminium compound and, (iii) one or more electron-donor compounds (external donor).

The alkylaluminium compound (ii) is preferably chosen among the trialkyl aluminium

compounds such as for example triethylaluminium, triisobutylaluminium, tri-n-

butylaluminium, tri-n-hexylaluminium, tri-n-octylaluminium. It is also possible to use mixtures

of trialkylaluminium's with alkylaluminium halides, alkylaluminium hydrides or

alkylaluminium sesquichlorides such as AlEt₂Cl and Al₂Et₃Cl₃.

The external donor (iii) can be of the same type or it can be different from the internal

donor of formula (I). Suitable external electron-donor compounds include the ethers, the esters,

the amines, heterocyclic compounds and particularly 2,2,6,6-tetramethyl piperidine, the ketones

and the 1,3-diethers of the general formula (II):

wherein R and R¹, R^π R , R^w and R^v equal or different to each other, hydrogen or hydrocarbon

radicals having from 1 to 18 carbon atoms, and R^VI and R^vn, equal or different from each other,

have the same meaning of R-R¹ except that they cannot be hydrogen; one or more of the R-R^vu groups can be linked to form a cycle.

Particularly preferred are the external donors chosen among silicon compounds of formula Ra⁵Rb⁶Si(OR⁷)c, where a and b are integer from 0 to 2, c is an integer from 1 to 4 and the sum

(a+b+c) is 4; R⁵, R⁶ and R⁷ are alkyl, cycloalkyl or aryl radicals with 1-18 carbon atoms. Particularly preferred are silicon compounds in which a is 1, b is 1 and c is 2. Among the

compounds of this preferred class, particularly preferred are the compounds in which R_ and/or

R are branched alkyl, cycloalkyl or aryl groups with 3-10 carbon atoms and R₇ is a Cj-Cio

alkyl group, in particular methyl. Examples of such preferred silicon compounds are

methylcyclohexyldimethoxysilane, diphenyldimethoxysilane, methyl-t-butyldimethoxysilane,

dicyclopentyldimethoxysilane. Moreover, are also preferred the silicon compounds in which a

is 0, c is 3 and R⁶ is a branched alkyl or cycloalkyl group and R⁷ is methyl. Examples of such

preferred silicon compounds are cyclohexyltrimethoxysilane, t-butyltrimethoxysilane and

thexyltrimethoxysilane.

The electron donor compound (iii) is used such an amount to give a molar ratio between

the organoaluminium compound and said electron donor compound (iii) of from 0,1 to 500

preferably from 1 to 300 and more preferably from 3 to 100. As previously indicated, when used in the (co)polymerization of olefins, and in particular of propylene, the catalysts of the

invention allow to obtain, with high yields, polymers having a high isotactic index (expressed

by high xylene insolubility X.I.), thus showing an excellent balance of properties. This is

particularly surprising in view of the fact that, as it can be seen from the comparison examples

herebelow reported, the use as internal electron donors of malonate compounds known in the

art gives poor results in term of yields and\or xylene insolubility thereby showing a very

insufficient balance of properties.

Therefore, it constitutes a further object of the present invention a process for the

(co)polymerization of olefins CH₂=CHR, in which R is hydrogen or a hydrocarbyl radical with 1-12 carbon atoms, carried out in the presence of a catalyst comprising the product of the

reaction between:

(i) a solid catalyst component comprising a titanium compound having at least a Ti-halogen bond, and an electron donor compound supported on a Mg halide in active form, in

(D:

wherein Ri is a Cι-C₂₀ linear or branched alkyl, C3-C20 alkenyl, C₃-C2₀ cycloalkyl, C -C ₀

aryl, arylalkyl or alkylaryl group; R is a C1-C20 linear alkyl, C3-C₂₀ linear alkenyl, C₆-C ₀ aryl, arylalkyl or alkylaryl group; R₃ and R₄ are independently selected from the group

consisting of Cι-C alkyl, cyclopropyl, with the proviso that when Ri is Cι-C₄ linear or

branched alkyl or alkenyl, R₂ is different from R_\; preferably R₂ is primary linear -C₂₀

alkyl or a primary C₆-C ₀ arylalkyl group.

(ii) an alkylaluminium compound and,

(iii) one or more electron-donor compounds (external donor).

Said polymerization process can be carried out according to known techniques for

example slurry polymerization using as diluent an inert hydrocarbon solvent, or bulk

polymerization using the liquid monomer (for example propylene) as a reaction medium.

Moreover, it is possible carrying out the polymerization process in gas-phase operating in one or more fluidized or mechanically agitated bed reactors.

The polymerization is generally carried out at temperature of from 20 to 120°C,

preferably of from 40 to 80°C. When the polymerization is carried out in gas-phase the operating pressure is generally between 0,5 and 10 MPa, preferably between 1 and 5 MPa. In

the bulk polymerization the operating pressure is generally between 1 and 6 MPa preferably

between 1,5 and 4 MPa. Hydrogen or other compounds capable to act as chain transfer agents

can be used to control the molecular weight of polymer.

The following examples are given in order to better illustrate the invention without

limiting it.

CHARACTERIZATIONS

The diethyl malonates of formula (I) used in the present invention can be prepared

according to known chemical synthesis as those described for example by J. March in

"Advanced Organic Chemistry" IV Ed. (1992) pp. 464-468. The malonates having R₃ and R different from ethyl can be prepared by

transesterification of the correspondent diethyl malonate as described in Example 1 of DE

2822472. Propylene general polymerization procedure

In a 4 litre autoclave, purged with nitrogen flow at 70°C for one hour, 80 ml of

anhydrous hexane containing 10 mg of solid catalyst component, 7 mmoles of AlEt₃ and 0.35

mmoles of dicyclopentyldimethoxysilane were introduced in propylene flow at 30C. The

autoclave was closed, 3 NL of hydrogen were added and then, under stirring, 1.2 Kg of liquid

propylene were fed. The temperature was raised to 70°C in five minutes and the polymerization was carried out at this temperature for two hours. The unreacted propylene was removed, the

polymer was recovered and dried at 70°C under vacuum for three hours, and then it was

weighed and fractionated with o-xylene to determine the amount of the xylene insoluble (X.I.) fraction at 25°C. Determination of X.I.

2.5 g of polymer were dissolved in 250 ml of o-xylene under stirring at 135°C for 30

minutes, then the solution was cooled to 25°C and after 30 minutes the insoluble polymer was

filtered. The resulting solution was evaporated in nitrogen flow and the residue was dried and

weighed to determine the percentage of soluble polymer and then, by difference, the X.I. %.

EXAMPLES

Examples 1-8 Preparation of Solid Catalyst Components

Into a 500 ml four-necked round flask, purged with nitrogen, 225 ml of TiCl were

introduced at 0°C. While stirring, 10.3 g of microspheroidal MgCl₂x2.1C H₅OH (obtained by partial thermal dealcoholation of an adduct prepared as described in ex. 2 of USP 4,399,054 but

operating at 3,000 rpm instead of 10,000) were added. The flask was heated to 40°C and 9

mmoles of malonate were thereupon added. The temperature was raised to 100°C and

maintained for two hours, then the stirring was discontinued, the solid product was allowed to

settle and the supernatant liquid was siphoned off.

200 ml of fresh TiCl₄ were added, the mixture was reacted at 120°C for one hour and

then the supernatant liquid was siphoned off. The solid was washed six times with anhydrous

hexane (6 x 100 ml) at 60°C and then dried under vacuum: the malonates used, the amount of Ti (wt%) and of malonates (wt%) contained in the solid catalyst component are reported in table 1. The polymerization results are reported in table 2.

Comparative Examples 9, 10 Preparation of Solid Catalyst Component

The catalyst components have been prepared according to the same procedure of the

examples 1-8 except for the fact that malonates different from those of formula (I) have been

used. The malonates used, the amount of Ti (wt%) and of malonates (wt % ) contained in the

solid catalyst component are reported in table 1. The polymerization results are reported in

table 2.

As it can be seen from the above, the use of the electron donor compounds of formula (I)

permit to obtain higher yields in the polymerization process with respect to the catalyst

containing the malonates known in the art. In particular it is very surprising the fact that by

changing for example from diethyl 2,2-diisobutyl malonate (comp. Ex. 9) to diethyl-2-n-

butyl-2-isobutyl malonate (Ex. 6) the yield in the polymerization process increases from 20.1

to 39.5 KgPP/gCat. Table 1

Table 2

Claims

1. A solid catalyst component for the polymerization of olefins CH₂=CHR in which R is

hydrogen or a hydrocarbyl radical with 1-12 carbon atoms, comprising a titanium

compound, having at least a Ti-halogen bond and an electron donor compound supported

on a Mg halide, in which said electron donor compound is selected from esters of

malonic acids of formula (I):

wherein Ri is a Cι-C₂o linear or branched alkyl, C₃-C₂o alkenyl, C₃-C₂o cycloalkyl, C₆-C₂o aryl, arylalkyl or alkylaryl group; R₂ is a Cι-C₂o linear alkyl, C₃-C₂o linear alkenyl, C₆-C₃o aryl, arylalkyl or alkylaryl group; R₃ and 1^ are independently selected from the group

consisting of C]-C alkyl, cyclopropyl, with the proviso that when Ri is Cj-C₄ linear or

branched alkyl or alkenyl, R₂ is different from Ri.

2. A solid catalyst component according to claim 1 in which R₂ is a -C₂₀ linear alkyl,

linear alkenyl, cycloalkyl, aryl, arylalkyl or alkylaryl group and R_\ is Cι-C₄ alkyl different

3. A solid catalyst component according to claim 1 in which at least Rj or R is primary C -

C₂₀ arylalkyl group.

. A solid catalyst component according to claim 1 in which the electron donor compound

of formula (I) is selected from the group consisting of: diethyl 2,2-dibenzylmalonate, ,

dimethyl-2-n-butyl-2-isobutylmalonate, diethyl-n-butyl-2-isobutylmalonate, diethyl-2-

isopropyl-2-n-butylmalonate, diethyl-2-methyl-2-isopropylmalonate, diethyl-2-methyl-2-

isobutylmalonate, diethyl 2-isobutyl-2-benzylmalonate.

5. A solid catalyst component according to claim 1 in which the magnesium halide is

MgCl₂ in active form.

6. A solid catalyst component according to claim 1 in which the titanium compound is TiCl₄ or TiCl₃.

7. A solid catalyst component according to claim 1 having a spherical form, a surface area between 20 and 500 m²/g, and a porosity higher than 0,2 cm³/g.

8. A catalyst for the polymerization of olefins CH₂=CHR, in which R is hydrogen or a

hydrocarbyl radical with 1-12 carbon atoms, comprising the product of the reaction

between:

(i) the solid catalyst component of claim 1 ;

(ii) an alkylaluminium compound and,

(iii) one or more electron-donor compounds (external donor).

9. Catalyst according to claim 8 in which the alkylaluminium compound (ii) is a trialkyl

aluminium compound.

10. Catalyst according to claim 9 in which the trialkyl aluminium compound is selected from

the group consisting of triethylalυminium, triisobutylaluminium, tri-n-butylaluminium,

tri-n-hexylaluminium, tri-n-octylaluminium.

1. Catalyst according to claim 8 in which the external donor (iii) is selected from the 1,3- diethers of the general formula (II):

(π)

wherein R and R¹, R^π R^πι, R^IV and R^v equal or different to each other, hydrogen or

hydrocarbon radicals having from 1 to 18 carbon atoms, and R^VI and R^vπ, equal or different from each other, have the same meaning of R-R¹ except that they cannot be hydrogen; one or more of the R-R^vπ groups can be linked to form a cycle.

12. Catalyst according to claim 8 in which the external donor (iii) is a silicon compound of

formula. Ra Rb Si(OR )c, where a and b are integer from 0 to 2, c is an integer from 1 to 4 and the sum (a+b+c) is 4; R⁵, R⁶ and R⁷ are alkyl, cycloalkyl or aryl radicals with 1-18

carbon atoms

13. Catalyst according to claim 12 in which a is 1, b is 1 and c is 2.

14. Catalyst according to claim 13 in which R₅ and/or R₆ are branched alkyl, cycloalkyl or

aryl groups with 3-10 carbon atoms and R₇ is a -Cio alkyl group, in particular methyl.

15. Catalyst according to claim 12 in which a is 0, c is 3 and R⁶ is a branched alkyl or

cycloalkyl group and R⁷ is methyl.

16. Catalyst according to claim 14 or 15 in which the silicon compound is selected from the

group consisting of methylcyclohexyldimethoxysilane, diphenyldimethoxysilane, methyl- t-butyldimethoxysilane, dicyclopentyldimethoxysilane cyclohexyltrimethoxysilane, t- butyltrimethoxysilane and thexyltrimethoxysilane.

17. Process for the (co)polymerization of olefins CH₂=CHR, in which R is hydrogen or a

hydrocarbyl radical with 1-12 carbon atoms, carried out in the presence of the catalyst of

claim 8.